I. Field of the Invention
The present invention is directed to a device which gives warning of the potential collapse of mine roofs. Specifically, the invention is concerned with a warning indicator that detects shifts in the ceiling of mines and provides warning thereof.
II. Description of the Prior Art
It is generally recognized that one of the most hazardous professions in modern society is that of being a miner. This is particularly true of those who work in underground coal mines. Not only is there serious health hazards, but many miners are killed or seriously injured by the collapse of the roofs of the mines. This problem has become so serious that new government mine safety regulations have been imposed.
There are several reasons why it has been impossible to develop a successful system that gives warning of impending cave-ins. A cave-in can potentially take place in any section of a mine. It is not unusual for a small mine to be composed of tunnels totalling over 25 miles. Thus, the area that must be monitored by any warning system is extremely extensive. Further, the tunneling system not only is not straight but does not maintain a constant elevation.
Several attempts have been made at developing warning devices which are suitable for use in mines. Emphasis has been placed on devices which utilize lights, visible chemical substances, and audio signals as warning devices. Examples of such devices are provided in U.S. Pat. Nos. 3,137,268, 3,111,655, and 3,786,503. Each of these devices requires constant maintenance and testing in order to insure that the devices are in operating condition. Due to the large number of devices which must be utilized in a mine, an expensive maintenance and testing program must be implimented. Such maintenance and testing programs are prohibitively expensive. Also, these devices are ineffective in areas of the mine which are only sporadically worked and in those situations where the device has already sounded its warning and no one was in the area to either see or hear it. The miners who later enter the area are totally unaware of the device's warning if the power source for the warning device has been exhausted.
There are other mechanical indicators, such as described in U.S. Pat. No. 2,725,843, which do not suffer the problems associated with an electrically operated warning device, however, these devices usually comprise plates which are bent by the sagging mine roof. In order to derive a warning from these devices each device must be constantly carefully examined to determine whether rock movement has occurred. Invariably these devices are not continually inspected nor closely monitored and therefore are of no value. Due to the number of warning units contained in a mine the type of monitoring program needed to make such a device effective is extremely expensive and so unfeasible.
The present invention is advantageous in that it provides a mine roof warning device which demonstrates high reliability and is inexpensive to construct. The device requires no maintenance and is simple to install on existing roof plates. Advantageously, the device does not utilize electrical systems and provides a visible warning signal which remains activated for indefinite periods. The mechanism does not require maintenance, testing, nor constant surveillance. The warning indicator is sensitive to the most minor movements of the rock layers above the mine.